1. Field of the Invention
The present invention relates to trench MOSFETs, or so-called UMOSFETs, and methods of making such trench MOSFETs, and more particularly the present invention relates to shielding the gate oxide of trench MOSFETs from high electric fields.
2. Description of the Background Art
Trench MOSFETs (metal oxide semiconductor field effect transistors), or so-called UMOSFETs, are used in high power electronic applications, and typically may be made of silicon or silicon-carbide (SiC). A problem with such devices is that the electric field created in the structure becomes increased or elevated at the bottom corners of the trench. Such increased or elevated electric field stresses the oxide near the corner of the device, resulting in poor device performance and/or device failure. A conventional solution to this problem is to increase the thickness of the gate oxide at the corner of the trench. This approach however does not decrease the electric field present at the corner of the trench, and also can lead to problems with the threshold voltage of the device. Thus, a key concern regarding trench MOSFET design is the reduction of the electric field present at the bottom corners of the trench so as to maintain stable operation of the device.